Method and Head-Up Display for the Perspective Transformation and Displaying of Image Content, and Vehicle

ABSTRACT

A method and a head-up display for the perspective transformation and displaying of rendered image content, as well as a corresponding vehicle, are provided. In the perspective transformation and displaying method, the image content to be displayed is subdivided into a plurality of tiles, and the individual tiles are each transformed in perspective using perspective transformation. The individual tiles that have been transformed in perspective are then combined to form a transformed image content, and the image content transformed in perspective is projected onto a projection area associated with the head-up display.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of PCT International Application No.PCT/EP2016/081358, filed Dec. 16, 2016, which claims priority under 35U.S.C. § 119 from German Patent Application No. 10 2016 204 044.8, filedMar. 11, 2016, the entire disclosures of which are herein expresslyincorporated by reference.

BACKGROUND AND SUMMARY OF THE INVENTION

The invention relates to a method and a head-up display for theperspective transformation and display of a rendered image content, andto a vehicle comprising such a head-up display.

Vehicles, in particular motor vehicles, generally comprise devices fordisplaying information. The information can both concern the operatingstate of the vehicle, for example the tank filling level, the speed, thestatus of the lighting system, etc., and facilitate operation of thevehicle for the driver, for example by displaying navigationinformation, displaying parking information, etc. In order to displaythe information to the driver as conveniently as possible, head-updisplays are used, which project the information to be displayed intothe driver's natural field of view, where the driver perceives itvisually as a virtual image. In this case, the natural field of viewcorresponds to the vehicle environment that is primarily to be takeninto consideration for the operation of the vehicle, in particular thecourse of the road ahead of the vehicle. When the information isprojected onto the windshield of the vehicle, for example, the drivercan read off the information without having to shift his/her gaze fromthe road, which increases safety when using the vehicle.

By virtue of curvatures of optical elements of the head-up display andthe windshield and the fact that the driver generally looks at thewindshield at an angle, the image of the information to be displayed isdistorted. In order to represent the information to the driver withoutdistortion, i.e. clearly and readily recognizably, the imaging of theinformation therefore has to be adapted to the beam path from theimage-generating device of the head-up display via optical elements ofthe head-up display and the windshield of the vehicle to the driver'seye.

For adaptation to the beam path, the information to be displayed istransferred as rendered image content to a graphics module (graphicsengine), which subjects the rendered image content to a transformation.The transformation is designed to compensate for the distortion thatarises in particular as a result of curved optical elements, a curvedwindshield and a non-perpendicular viewing angle with respect to thewindshield. In other words, the rendered image content is distorted bythe transformation of the graphics module in order to enable theobserver, in particular the driver, to visually perceive a rectifiedimage of the rendered image content.

It is an object of the invention to specify a method, a head-up displayand a vehicle in which the transformation and display of a renderedimage content is carried out more flexibly and more rapidly and thetransformation can be adapted in particular more easily to changes ofthe beam path, for example by a change in the position of the image onthe projection surface.

In the case of the method for the perspective transformation and displayof a rendered image content by a head-up display, in accordance with afirst aspect of the invention, the rendered image content, i.e. imagecontent to be displayed, is divided into a plurality of regions, inparticular tiles or rectangles. The tiles, or the image contentcontained in the individual tiles, are or is preferably transformed ineach case by means of a perspective transformation and the individual,perspectively transformed tiles, or perspectively transformed imagecontents contained in the perspectively transformed tiles, are joinedtogether to form a perspectively transformed image content. Theperspectively transformed image content is projected onto a projectionsurface assigned to the head-up display.

The head-up display according to the invention for the perspectivetransformation and display of a rendered image content in accordancewith a second aspect of the invention comprises a control unit and aprojection unit. In particular, the head-up display according to theinvention is configured to carry out the perspective transformation anddisplay of a rendered image content according to the first aspect of theinvention. Preferably, the control unit comprises a first module,configured for dividing the rendered image content, i.e. image contentto be displayed, into a plurality of regions, in particular tiles orrectangles, a second module, in particular a graphics module, configuredfor transforming the individual tiles, or the image content contained inthe individual tiles, by means of a respective perspectivetransformation, in particular via a graphics programming interface, anda third module, configured for combining the individual, perspectivelytransformed tiles to form a transformed image content. Furthermore, theprojection unit is preferably configured for projecting theperspectively transformed image content onto a projection surfaceassigned to the head-up display.

The first, second and third modules can be embodied in each case ashardware or software module. In particular, one or two modules can beembodied as software module and the remaining module(s) can be embodiedas hardware module.

Preferably, a first, second or third module embodied as software moduleis implemented on one or more processors, in particular centralprocessing unit or central processing units (CPU) of the control unit.

The vehicle according to the invention in accordance with a third aspectof the invention comprises a head-up display in accordance with thesecond aspect of the invention.

The features and advantages described with regard to the first aspect ofthe invention and the advantageous configuration thereof are alsoapplicable to the second aspect and the third aspect of the inventionand the advantageous configurations thereof, and vice versa.

The invention is based on the approach of dividing an image to bedisplayed, in particular a rendered image content, which containsinformation to be displayed, into a plurality of regions, for exampletiles, in particular rectangles or rectangular tiles, and transformingsaid regions separately by a respective perspective transformation. Inother words, the perspective transformation of the image, i.e. of therendered image content, is carried out modularly. Afterward, theperspectively transformed regions, i.e. tiles, are combined again toform a now perspectively transformed image or image content, which, inor by a head-up display, is projected onto a projection surface, and canbe visually perceived by an observer, in particular a driver in avehicle comprising a head-up display, without distortion, i.e. clearlyand readily recognizably, on account of the perspective transformationperformed.

In this case, the perspective transformation of individual tiles ispreferably coordinated with the respective individual tile to beperspectively transformed. If a change in the beam path of the head-updisplay necessitates the adaptation of the image to be displayed, i.e.of the rendered image content, this can be brought about by coordinationor adaption of individual perspective transformations. In particular, itis not necessary to coordinate or to adapt each individual one of theperspective transformations, or to perform an adaptation, i.e. change,of a single perspective transformation that transforms the entire imageto be displayed, i.e. the entire rendered image content. This generallyrequires a high computing power and therefore reduces the frame rate atwhich the transformed images can be displayed by the head-up display.

Preferably, the invention makes it possible in particular to dispensewith the perspective transformation of individual tiles if this is notnecessary for a distortion-free representation or display of thecombined and transformed image, i.e. image content. Particularly if onlya portion of the image to be displayed, i.e. of the rendered imagecontent, has to be distorted or rectified by means of a perspectivetransformation or transformation for adaptation to the beam path of thehead-up display or the observer's position, by means of the modularperspective transformation it is possible to reduce the computationalcomplexity for perspective distortion or rectification by nottransforming individual tiles whose image content does not have to beadapted to the beam path.

Preferably, the perspective transformation of individual tiles, i.e. amodular perspective transformation, furthermore allows a memory- andcomputation-time-saving perspective transformation by means of agraphics module, which is preferably in widespread use and runs stablyin particular on current microprocessors, in particular on differentplatforms. With further preference, said graphics module is designed toprocess vector graphics in particular with hardware acceleration, suchthat it is possible to carry out individual perspective transformationson a vector basis particularly rapidly and efficiently.

Overall, the invention enables rapid and flexible transformation anddisplay of a rendered image content.

In one advantageous configuration of the method for the perspectivetransformation display of a rendered image content, during thetransformation each individual tile is perspectively transformed withregard to at least one of the following features: trapezoid shape,curvature, stretching and/or compression, rotation, offset. Inparticular, each individual tile can also be perspectively transformedby means of a combination of at least two of these features. A reliableadaptation of the image content to be displayed to the beam path of thehead-up display is possible as a result.

In a further advantageous configuration of the method for theperspective transformation and display of a rendered image content,adjoining tiles have overlapping image contents. In particular, theoverlapping image contents each have a width of one, two or threepixels. This ensures that the perspectively transformed tiles, duringthe process of combining to form a perspectively transformed imagecontent, likewise have overlapping, perspectively transformed imagecontent or the edges of the perspectively transformed tiles terminateflush, in particular. In particular, this reliably prevents thecombined, perspectively transformed image content from having regionswhich are not covered by at least one perspectively transformed tile andare therefore represented as color-neutral, in particular black orwhite, pixels. Preferably, this feature of the method also prevents saidregions from arising by means of applying an edge smoothing, inparticular by means of a smoothing filter.

In a further advantageous configuration of the method for theperspective transformation and display of a rendered image content, theimage content is present as raster graphics, wherein individual pixelsof a tile are displaced by the perspective transformation. As a result,the rendered image content can be divided particularly easily intodifferent regions, preferably tiles or rectangles or rectangular tiles,wherein in each case a predefined number of pixels of the rastergraphics are assigned to a region, or to a tile. The individual pixelsof the raster graphics that belong to a respective tile are displaced bythe perspective transformation. Consequently, the perspectivetransformation can be realized particularly easily.

Preferably, the raster graphics have a specific color depth, inparticular 32, 24, 16, 8 or 4 bits. With further preference, the rastergraphics can also have a color depth that lies between these values.With further preference, the raster graphics can also have a color depththat is greater than 32 bits or less than 4 bits. With furtherpreference, different pixels of the raster graphics each have differentcolor depths. In particular, preferably, some contiguous pixels of theraster graphics which respectively belong to an individual tile have ineach case the same color depth. Particularly preferably, the color depthof an individual tile has a magnitude only such as is necessary for thetrue-color representation of the image content contained in theindividual tiles. As a result, the rendered image content requiresparticularly little memory space, in particular in a buffer memory, andthe perspective transformations of the tiles can be carried outparticularly efficiently.

In a further advantageous configuration of the method for theperspective transformation and display of a rendered image content, aninterpolation, in particular a linear interpolation, of individualpixels of a tile, in particular of the pixels which adjoin pixelsdisplaced by the perspective transformation and/or lie between saidpixels, is carried out during the perspective transformation. Thisreliably avoids the situation in which regions having pixels to which nocolor value was assigned arise. Preferably, the number of pixels pertile is low, such that individual pixels are not displaced over largedistances during the perspective transformation. In this case, inparticular, a linear interpolation of the pixels lying between thepixels displaced during the perspective transformation yields aperspectively transformed image content whose image generated by ahead-up display can be visually perceived distinctly and clearly, i.e.in particular without artifacts. A linear interpolation causes inparticular only a low computational complexity, that is to say that theburden for a calculating processor is low, for which reason theperspective transformation can be carried out rapidly and efficiently.

In a further advantageous configuration of the method for theperspective transformation and display of a rendered image content, theindividual tiles are perspectively transformed by multiplication by atransformation matrix. Multiplication by a transformation matrix is aparticularly simple and precise way of carrying out a transformation. Acorresponding perspective transformation can therefore be carried outparticularly rapidly and efficiently, in particular by a graphicsmodule. In particular, it is therefore possible to achieve, for theframe rate at which rendered image contents are perspectivelytransformed, a value of 30 to 90, preferably of 45 to 75, particularlypreferably of substantially 60, perspectively transformed image contentsper second. In one particularly advantageous configuration of themethod, it is possible to achieve a value of 90 to 160, preferably ofsubstantially 120, perspectively transformed image contents per second.

Preferably, during the matrix multiplication by a transformation matrix,the positions of individual pixels of a tile, in particular of the fourcorner points, which are preferably given by support vectors, aremultiplied by the transformation matrix. In this case, support vectorsare vectors which specify the position of a pixel relative to an origin,wherein the origin may be in particular a corner point or midpoint of atile or of the image, i.e. of the rendered image content. As a result ofthe multiplication of the support vectors by the transformation matrix,the position of the individual pixels of the tile shifts relative to theorigin. Preferably, pixels which lie between these displaced pixels, inparticular in a manner adjoining the latter, are interpolated, inparticular by a linear interpolation. Preferably, gaps in the imagecontent of the perspectively transformed tile are closed as a result.

Preferably, by means of the choice of the number and/or the dimensions,i.e. the size or area, of the tiles when dividing the image content tobe displayed, the number of pixels to be interpolated linearly, inparticular, can be determined, in particular limited, since the numberof pixels per tile that have to be perspectively transformed decreasesas the number of tiles increases. This ensures that in particular alinear interpolation of pixels that lie between displaced pixels, inparticular in a manner adjoining displaced pixels, generates clear anddistinct, perspectively transformed image content on the tiles or thecombined perspectively transformed image content to be displayed via thehead-up display, i.e. perspectively transformed image content withoutartifacts.

Preferably, the number and/or the dimensions of the tiles are/is chosento be greater than a critical number and/or size for which the number ofpixels to be interpolated linearly, in particular, is so small thatartifacts, in particular corners, occur in the perspectively transformedimage content. This ensures that the combined, perspectively transformedimage content to be displayed via the head-up display has no artifacts,in particular corners. Preferably, the number and/or size of the tilesare/is chosen such that the tiles overlap, in particular in each casewith one or two pixels.

In a further advantageous configuration of the method for theperspective transformation and display of a rendered image content, thetransformation matrix is chosen from a multiplicity of transformationmatrices. In particular, the multiplicity of transformation matriceshere preferably includes in each case a transformation matrix for eachtile to be perspectively transformed. This can ensure that thetransformation matrices are adapted to the beam path of the imaging ofthe tile to be perspectively transformed in each case, or can be adaptedin particular individually to changes in the beam path of the imaging ofthe tile to be perspectively transformed in each case. With furtherpreference, the multiplicity of transformation matrices includes variousperspective transformations.

Any vectorial perspective transformation can be realized by the use oftransformation matrices. As a result, the perspective transformation canbe adapted particularly well to the beam path. Particularly preferably,the perspective transformation carried out with a transformation matrixfrom the multiplicity of transformation matrices relates to at least oneof the following features: trapezoid shape, curvature, stretching and/orcompression, rotation, offset.

In a further advantageous configuration of the method for theperspective transformation and display of a rendered image content, theperspective transformation of the individual tiles is carried out by agraphics module, preferably via a graphics programming interface, inparticular OpenVG. The use of a graphics module significantlyaccelerates the perspective transformation of the individual tiles, inparticular by means of hardware acceleration, and reduces thecomputational burden for a central processing unit (CPU). Preferably, agraphics programming interface is used which is in widespread use and isavailable as standard on microprocessors. With further preference, thegraphics programming interface is available on a plurality of platforms.Furthermore, the graphics programming interface used preferably allowsthe use of a graphics module which makes available thehardware-accelerated processing or calculation of vector graphics.

In a further advantageous configuration of the method for theperspective transformation and display of a rendered image content, theperspectively transformed tiles are stored in a buffer memory. Thebuffer memory allows particularly fast access to the perspectivelytransformed tiles stored therein, in particular during the process ofcombining to form an entire perspectively transformed image, or imagecontent, to be displayed.

In a further advantageous configuration of the method for theperspective transformation and display of a rendered image content, onlya portion of the plurality of tiles is perspectively transformed and theremaining transformed tiles are loaded from the buffer memory for thepurpose of combining the transformed image. As a result, the combinationof the perspectively transformed image, or image content, to bedisplayed can be significantly accelerated. In particular, it is thuspossible to achieve a frame rate at which rendered image content isperspectively transformed of 30 to 90, preferably of 45 to 75,particularly preferably of substantially 60, perspectively transformedimage contents per second. In one particularly advantageousconfiguration of the method, it is possible to achieve a value of 90 to160, preferably of substantially 120, perspectively transformed imagecontents per second.

In a further advantageous configuration of the method for theperspective transformation and display of a rendered image content, onlythat portion of the plurality of tiles is perspectively transformedwhich contains elements of the image content which have changed withrespect to an image content that was previously to be transformed and tobe displayed. In particular, the remaining perspectively transformedtiles required for combining the perspectively transformed tiles to forma perspectively transformed image content to be displayed are loadedfrom the buffer memory. This ensures, in particular, that a processordemanded by the perspective transformations processes only those partsof the rendered image content which differ from the image content thatwas previously perspectively transformed and displayed, i.e. containchanged information to be displayed or a changed representation of theinformation to be displayed, as a result of which the computing power ofsaid processor is significantly reduced in comparison with carrying outa perspective transformation of all the tiles. As a result, thecomputing power of such a processor can be allocated particularlyefficiently for calculations and a frame rate at which rendered imagecontent is perspectively transformed of 30 to 90, preferably of 45 to75, particularly preferably of substantially 60, perspectivelytransformed image contents per second can be achieved. In oneparticularly advantageous configuration of the method, it is possible toachieve a value of 90 to 160, preferably of substantially 120,perspectively transformed image contents per second.

In a further advantageous configuration of the method for theperspective transformation and display of a rendered image content,different portions of the plurality of tiles have different colordepths, in particular 32, 24, 16, 8 and 4 bits. With further preference,different parts of the plurality of tiles can also have a color depththat lies between these values. With further preference, different partsof the plurality of tiles can also have a color depth that is greaterthan 32 bits or less than 4 bits. In particular, the tiles have in eachcase the smallest possible color depth for which the respectivelycontained image content can still be displayed or represented with truecolor, i.e. with no reduction in color quality. Preferably, theperspective transformations, in particular the preferably linearinterpolations of individual pixels, of the plurality of tiles havingthe different color depths are carried out at the respective color depthof the tile that is to be perspectively transformed. This ensures thatthe perspective transformation or the perspectively transformed tilerequires only little memory space or the preferably linear interpolationrequires little computation demand. As a result, the perspectivetransformations, in particular the preferably linear interpolations ofindividual pixels, can be carried out particularly rapidly andefficiently.

In a further advantageous configuration of the method for theperspective transformation and display of a rendered image content, theplurality of tiles are mirrored by a point or line mirroring during theperspective transformation and are combined to form a perspectivelytransformed, mirrored image content. As a result, the image orientationof the perspectively transformed image content to be displayed can beadapted to the beam path of the head-up display. In particular, themirroring makes it possible to dispense with the use of additionaloptical elements in the head-up display which change, in particularrotate and/or mirror, the image orientation of the perspectivelytransformed image content for error-free imaging on the projectionsurface of the head-up display. As a result, the head-up display obtainsa particularly simple structure.

Other objects, advantages and novel features of the present inventionwill become apparent from the following detailed description of one ormore preferred embodiments when considered in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows one embodiment of the method of the present invention forthe transformation and display of a rendered image content by a head-updisplay.

FIG. 2 shows an illustration of a rendered image content divided into aplurality of tiles by one embodiment of the method according anembodiment of the invention.

FIG. 3 shows an illustration of a perspective transformation of a tileaccording an embodiment of the invention.

FIG. 4 shows an illustration of an image content transformed byperspective transformations of individual tiles by one embodiment of themethod according to the invention.

FIG. 5 shows illustrations of several results of basic perspectivetransformations in accordance with embodiments of the invention.

FIG. 6 shows an illustration of a grid and a distorted grid inaccordance with an embodiment of the invention.

FIG. 7 shows an illustration of envelopes of support points on aprojection surface in accordance with an embodiment of the invention.

DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 1 shows one embodiment of the method 100 for the transformation anddisplay of a rendered image content 1 by a head-up display, which isexplained below with reference to the further figures.

FIG. 2 shows an illustration of a rendered image content 1 divided intoa plurality of tiles 2 by one embodiment of the method 100 according tothe invention. The image content 1 contains a plurality of elements 7,8, 9, 10, which indirectly and/or directly concern the operation of thevehicle, in particular traffic regulations 7 to be complied with,warning indications 8, navigation information 9 and/or speed information10. An element 7, 8, 9, 10 is in each case a portion of the entire imagecontent 1. The elements 7, 8, 9 are preferably displayed and/orrepresented, or imaged, as pictograms. With further preference, theelements 9, 10 are displayed and/or represented, or imaged, as textcharacters and/or lettering, in particular number characters. The imagecontent 1 is preferably rendered, such that it is present as a digitalimage, in particular as raster graphics. As a result, the image content1 can easily be processed, i.e. changed and/or modified, in particulardistorted, by digital methods, in particular transformations, preferablyperspective transformations.

The rendered image content 1 is divided into a plurality of regions, inparticular tiles 2, preferably rectangular tiles 2, in method step 101.With further preference, the tiles 2 are square. The edges of the tiles2 are marked by horizontal and vertical lines 11 in the exemplaryembodiment shown, for the sake of better clarity.

Preferably, individual tiles 2 enclose individual elements 7, 8, 9, 10or portions of the elements 7, 8, 9, 10, i.e. that portion of the entireimage content 1 which is contained in the individual tiles 2 representsindividual elements 7, 8, 9, 10 or portions of the elements 7, 8, 9, 10.

Preferably, different tiles 2 have different color depths, in particular32, 24, 16, 8 or 4 bits. With further preference, different tiles canalso have a color depth that lies between these values. With furtherpreference, different tiles can also have a color depth that is greaterthan 32 bits or less than 4 bits. With further preference, the colordepth of a tile 2 has a magnitude only such as is necessary for clearand distinct, i.e. true-color, representation of that portion of theimage content 1 which is contained in the tile 2. In particular, tiles 2that contain no elements 7, 8, 9, 10 of the image content 1 have aparticularly low color depth, for example 4 bits or 1 bit. Preferably,tiles 2 that contain single-colored elements 7, 8, 9, 10 orsingle-colored portions of the elements 7, 8, 9, 10, in particular textcharacters or lettering and/or number characters, have a low colordepth, in particular 16, 8 or 4 bits, or a value between these values.The memory space of the rendered image content 1 or of the individualtiles 2 can be significantly reduced as a result.

FIG. 3 shows an illustration of a perspective transformation 3 of a tile2. In method step 102, the perspective transformation 3 generates aperspectively transformed tile 4 from a, preferably rectangular, inparticular square, tile 2.

Preferably, the perspective transformation 3 is implemented by a matrixmultiplication, in particular the multiplication by a transformationmatrix, in method step 102. In this case, the individual pixels, inparticular the four corner points, of the tile 2 which are indicated bysupport vectors, said tile preferably being present as raster graphics,are multiplied by a matrix that generates a perspective transformation.Support vectors are vectors that specify the position of the pixels withrespect to an origin, in particular with respect to one of the fourcorners of the tile 2 or of the image composed of the tiles 2, i.e. therendered image content 1 or the midpoint of the tile 2 or of the imagecomposed of the tiles 2, i.e. the rendered image content 1.

As a result of the perspective transformation 3, in particular as aresult of the multiplication of the support vectors by a transformationmatrix, in the exemplary embodiment shown, the four corner points of thetile 2 are assigned a new positon in method step 102, indicated by thefour dashed arrows 12. In particular, magnitude, i.e. length, anddirection, i.e. orientation, of the support vectors of the pixels to beperspectively transformed change in this case.

If the perspective transformation 3 in method step 102 gives rise togaps between the pixels of the perspectively transformed tile 4, saidgaps are preferably closed by an interpolation, in particular by alinear interpolation, in method step 103. In particular, pixels whichadjoin and/or lie or are arranged between pixels displaced by theperspective transformation 3 are assigned a value by the interpolation,such that the perspectively transformed tile 4 has a gap-free portion ofthe transformed image content 5, i.e. is representable withoutartifacts. Preferably, a smoothing of the perspectively transformedimage content is carried out by the linear interpolation in method step103, such that said image content is representable in a manner free ofartifacts by a head-up display.

FIG. 4 shows an illustration of a transformed image content 5 that wascombined by one embodiment of the method 100 according to the inventionand was produced in method step 104 by perspective transformations 3 ofindividual tiles 2 in method step 102. For the sake of better clarity,the edges of the perspectively transformed tiles 4 are shown bysubstantially horizontal and substantially vertical lines 11 as in FIG.1.

Individual tiles 2 are transformed by respectively different perspectivetransformations 3, in particular respectively different transformationmatrices, i.e. modularly, during the perspective transformation 3 inmethod step 102 and are combined to form a perspectively transformedimage content 5 in method step 104. In method step 105, theperspectively transformed image content 5 is preferably projected by ahead-up display onto a projection surface assigned to the head-updisplay, where it is visually perceived by a user, in particular thedriver of the vehicle equipped with the head-up display, as anundistorted image.

As a result of the separate, i.e. modular, perspective transformation 3in method step 102, each perspectively transformed tile 4 preferablyacquires a different shape than adjoining perspectively transformedtiles 4. In particular, this results in a closed or continuous,preferably artifact-free, transformed image content 5 that can berepresented or displayed as a closed or continuous, preferablyartifact-free, image. Preferably, by means of the separate perspectivetransformations 3, adjoining tiles 2 are perspectively transformed in amanner such that their edges adjoin one another in a closed, i.e. flush,manner. With further preference, for each tile 2 a perspectivetransformation 3 is chosen from a multiplicity of perspectivetransformations 3, or the perspective transformation 3 is adapted, inparticular separately, for each tile 2, such that after the perspectivetransformation 3 and combination with adjacent perspectively transformedtiles 4, a closed, artifact-free, perspectively transformed imagecontent 5 results. In particular, the respective perspectivetransformations 3 are chosen or adapted for individual tiles 2 such thatafter combination to form the perspectively transformed image content 5,no edges, bends, discontinuities and/or noise occur(s) in theperspectively transformed image content 5 or the representable,perspectively transformed image.

With further preference, the rendered image content 1 is divided intotiles 2 having overlapping edges in method step 101 before theperspective transformation 3, i.e. a portion of the rendered imagecontent 1 is represented by more than one tile 2 or is contained in morethan one tile 2. In particular, the edges of adjoining tiles 2 overlap.The overlapping edges, i.e. the overlapping region, can have differentwidths, in particular 1, 2, 3 or more pixels. With further preference,the width of the overlapping edges is chosen or adapted such that duringthe process of combining the perspectively transformed tiles 4 to form aperspectively transformed image content 5 in method step 104, eachregion of the perspectively transformed image that is representable ordisplayable and/or imageable by the perspectively transformed imagecontent 5 is covered by at least one perspectively transformed tile 4.As a result, the edges of the perspectively transformed tiles 4 need notadjoin one another in a closed, i.e. flush, manner, with the result thatthere is greater freedom in the choice of the appropriate perspectivetransformations 3 for an individual tile 2, or the adaptation of theperspective transformation 3 to an individual tile 2. In particular, asa result, perspectively transformed tiles 4 have to adjoin one anotheronly in a substantially closed, i.e. flush, manner.

Preferably, during the process of combining to form a perspectivelytransformed image content 5 in method step 104, the overlapping regionor the overlapping edges of the perspectively transformed tiles 4 is orare smoothed, in particular averaged or interpolated, in a manner suchthat a seamless transition between adjoining perspectively transformedtiles 4 results. Artifacts, in particular edges, bends, discontinuitiesand/or noise, in the combined perspectively transformed image content 5are avoided particularly reliably as a result.

FIG. 5 shows several results of basic perspective transformations 3.

FIG. 5A shows the result of a perspective transformation 3 whichperspectively transforms a rectangular tile 2 into a trapezoidal tile.

FIG. 5B shows the result of a perspective transformation 3 whichperspectively transforms a rectangular tile 2 into aparallelogram-shaped tile. This is a special case of FIG. 4A.

FIG. 5C shows the result of a perspective transformation 3 whichperspectively transforms a rectangular tile 2 into a curved orbarrel-shaped tile having two convex opposite sides.

FIG. 5D shows the result of a perspective transformation 3 whichperspectively transforms a rectangular tile 2 into a curved or twistedtile having a convex and a concave opposite side. This is a special caseof FIG. 5C.

FIG. 5E shows the result of a perspective transformation 3 whichperspectively transforms a rectangular tile 2 into a compressed orstretched tile.

FIG. 5F shows the result of a perspective transformation 3 whichperspectively transforms a rectangular tile 2 into a tile that isrotated, i.e. turned by a specific angle, in particular in relation tothe rectangular tile 2.

Preferably, the perspective transformation 3 of an individual tile 2 iscomposed of a plurality of basic perspective transformations 3, theresults of which are shown in FIGS. 5A to F. As a result, it ispossible, for each individual tile 2, to choose a perspectivetransformation 3 from a multiplicity of perspective transformations 3 orto adapt the perspective transformation 3 such that after the process ofcombining the perspectively transformed tiles 4 in method step 104, aparticularly artifact-free, perspectively transformed image content 5,which in particular is free of edges, bends, discontinuities and/ornoise, results.

In order to determine the manner in which a rendered image content 1 hasto be perspectively transformed in method step 102 in order to bedisplayed to the driver of a vehicle as an undistorted image in methodstep 105, i.e. the manner in which a rendered image content 1 has to beadapted to the beam path of the head-up display, i.e. from theimage-generating unit of the head-up display via the projection surfaceto the driver's eye, a regular, in particular conventional, grid 13 isdistorted, such that the distortion corresponds to the adaptation to thebeam path.

FIG. 6 shows an illustration of a regular grid 13 (upper part of thefigure) and of a distorted grid 14 resulting from the distortion (lowerpart of the figure). The grid points 15 of the regular grid 13,illustrated as crosses, are used or taken into account when dividing therendered image content 1 into a plurality of tiles 2. The grid points 16of the distorted grid 14, illustrated as dots, are used or taken intoaccount when selecting the appropriate perspective transformation 3 oradapting the perspective transformation 3 of an individual tile 2 thatis to be perspectively transformed. This reliably ensures that theperspective transformation of the rendered image content 1 in methodstep 102 corresponds to the adaptation to the beam path of the head-updisplay.

Preferably, the distortion of the regular grid 13, i.e. the conversioninto a distorted grid 14, is performed by a perspective transformation 3or a combination of the basic perspective transformations 3, the resultsof which are shown in FIG. 4.

With further preference, the grid points 15 of the regular grid 13indicate the position of the tiles 2. With further preference, the gridpoints 16 of the distorted grid 14 indicate the position of theperspectively transformed tiles 4. In particular, the grid points 15 ofthe regular grid 13 function as initial support points of the tiles 2,preferably as the midpoint thereof or one of their corner points. Inparticular, the grid points 16 of the distorted grid 14 function astarget support points of the perspectively transformed tiles 4,preferably as the midpoint thereof or one of their corner points.

FIG. 7 shows an illustration of the distribution of regular anddistorted grids 13, 14 on an image-generating unit. The image-generatingunit is designed to represent or to image image content as image on adisplay 6 in method step 105. From the display 6, preferably only aspecific transformation region 17, represented by the dashed line, isprovided for representing or imaging the perspectively transformed imagecontent 5. The perspective transformations 3 of the individual tiles 2are preferably chosen or adapted such that in method step 102perspectively transformed image content 5 does not project beyond thetransformation region 17.

The position of the grid points 16 of the distorted grid 14 preferablylies within a target region 18, illustrated by a thin dotted line, whichin particular is part of the transformation region 17. The target region18 functions as envelope of the grid points 16 of the distorted grid orof the target support points of the perspectively transformed tiles 4.The target region 18 is preferably smaller than the transformationregion 17 since the perspectively transformed tiles 4 have a lateralextent, and this prevents perspectively transformed tiles 4 and thusparts of the perspectively transformed image content 5 from projectingbeyond the transformation region 17.

The position of the grid points 15 of the regular grid 13 is displayedby the initial region 19, illustrated by a solid thin line. The initialregion functions as envelope of the grid points 15 of the regular grid13 or of the initial support points of the tiles 2. The initial region19 is preferably smaller than the transformation region 17 since theposition of individual tiles 2 can be displaced by the perspectivetransformation 3 toward the edge of the display 6 or toward the edge ofthe transformation region 17 or the lateral extent of individual tiles 2can increase. This reliably ensures that rendered image content 1divided into a plurality of tiles 2 does not project beyond the display6 or the transformation region 17 of the display 6 after the perspectivetransformation 3 and combination of the individual tiles 2 to form aperspectively transformed image content 5.

The foregoing disclosure has been set forth merely to illustrate theinvention and is not intended to be limiting. Since modifications of thedisclosed embodiments incorporating the spirit and substance of theinvention may occur to persons skilled in the art, the invention shouldbe construed to include everything within the scope of the appendedclaims and equivalents thereof.

LIST OF REFERENCE SIGNS WHERE APPROPRIATE

-   1 Rendered image content-   2 Tile-   3 Perspective transformation-   4 Perspectively transformed tile-   5 Transformed image content-   6 Display-   7 Traffic regulations-   8 Warning indication-   9 Navigation information-   10 Speed information-   11 Tile edge-   12 Arrow-   13 Regular grid-   14 Distorted grid-   15 Grid point of the regular grid-   16 Grid point of the distorted grid-   17 Transformation region-   18 Target region-   19 Initial region-   100 Method for the perspective transformation and display of a    rendered image content by a head-up display-   101 Dividing the rendered image content into a plurality of tiles-   102 Perspectively transforming a plurality of tiles-   103 Interpolation-   104 Combining perspectively transformed tiles to form a    perspectively transformed image content-   105 Projecting perspectively transformed image content onto a    projection surface by means of a head-up display

What is claimed is:
 1. A method for perspective transformation anddisplay of a rendered image content by a head-up display, comprising theacts of: dividing the rendered image content into a plurality of tiles;transforming individual ones of the plurality of tiles by a respectiveperspective transformation into individual perspectively transformedtiles; combining the individual perspectively transformed tiles into aperspectively transformed image content; and projecting theperspectively transformed image content onto a projection surfaceassigned to the head-up display.
 2. The method as claimed in claim 1,wherein during the perspective transforming act each tile of individualones of the plurality of tiles is perspectively transformed with regardto one or more of the following features: trapezoid shape, curvature,stretching, compression, rotation, and offset.
 3. The method as claimedin claim 2, wherein adjoining tiles of the plurality of tiles haveoverlapping image contents.
 4. The method as claimed in claim 2, whereinthe rendered image content is in the form of raster graphics, andindividual pixels of the individual ones of the plurality of tiles aredisplaced by the perspective transformation.
 5. The method as claimed inclaim 4, wherein during the perspective transforming act, interpolationis performed between at least a portion of adjoining ones of theindividual pixels of the individual ones of the plurality of tiles. 6.The method as claimed in claim 5, wherein during the perspectivetransforming act, the individual ones of the plurality of tiles areperspectively transformed by multiplication by a transformation matrix.7. The method as claimed in claim 6, wherein the transformation matrixis chosen from a plurality of predetermined transformation matrices. 8.The method as claimed in claim 2, wherein during the perspectivetransforming act, the perspective transformation of the individual onesof the plurality of tiles is carried out by a graphics module via agraphics programming interface.
 9. The method as claimed in claim 2,further comprising the act of: storing the perspectively transformedtiles in a buffer memory.
 10. The method as claimed in claim 9, whereinonly a portion of the individual ones of the plurality of tiles isperspectively transformed, and during the act of combining theindividual perspectively transformed tiles, perspectively transformedtiles corresponding to the remaining the individual ones of theplurality of tiles retrieved from the buffer memory are combined withthe portion the individual ones of the plurality of tiles isperspectively transformed to form the perspectively transformed imagecontent.
 11. The method as claimed in claim 10, wherein the portion ofthe individual ones of the plurality of tiles perspectively transformedinclude the individual ones of the plurality of tiles having elements ofthe image content changed with respect to image content previouslystored in the buffer.
 12. The method as claimed in claim 1, whereindifferent portions of the plurality of tiles have different colordepths.
 13. The method as claimed in claim 1, wherein during theperspective transformation act, the plurality of tiles are mirrored by apoint or line mirroring, and during the combining act are combined toform a perspectively transformed, mirrored image content.
 14. A head-updisplay for the perspective transformation and display of a renderedimage content, comprising: a control unit including a first moduleconfigured to divide the rendered image content into a plurality oftiles, a second module configured to transform individual ones of theplurality of tiles by perspective transformation, and a third moduleconfigured to combine the individual perspectively transformed tilesinto a transformed image content; and a projection unit configured toproject the perspectively transformed image content onto a projectionsurface assigned to the head-up display.
 15. A vehicle, comprising: avehicle front window; and a head-up display including a control unitincluding a first module configured to divide the rendered image contentinto a plurality of tiles, a second module configured to transformindividual ones of the plurality of tiles by perspective transformation,and a third module configured to combine the individual perspectivelytransformed tiles into a transformed image content; and a projectionunit configured to project the perspectively transformed image contentonto the vehicle front window.